V-type internal combustion engines have a rail or bank of cylinders on a first side, i.e., the A side and also on a second side, i.e., the B side, for temporary storage of the fuel. The injectors, which are connected to the rail, inject the fuel into the combustion chambers. In a first design of the common rail system a single high pressure pump pumps the fuel in parallel into both rails by increasing the pressure conditions. Therefore, both rails exhibit the same rail pressure. A second design of the common rail system differs from the first design in that a first high pressure pump pumps the fuel into a first rail; and a second high pressure pump pumps the fuel into a second rail. Both designs are known, for example, from DE 43 35 171 C1.
Since the quality of the combustion depends crucially on the pressure level in the rail, this pressure level may be automatically controlled. Typically a closed loop rail pressure control circuit comprises a pressure controller, the suction throttle with a high pressure pump and the rail as the controlled system, as well as a software filter in the feedback branch. In this closed loop rail pressure control circuit the pressure level in the rail corresponds to the correcting variable. The measured raw values of the rail pressure are converted by the filter to an actual rail pressure and compared with a set rail pressure. Then the resulting system deviation is converted by means of the pressure controller into an actuating signal for the suction throttle. The actuating signal corresponds to a volume flow in units of liters per minute. This actuating signal is implemented electrically as a PWM (pulse width modulated) signal. A corresponding closed loop rail pressure control circuit is known from DE 10 2006 049 266 B3.
DE 10 2007 034 317 A1 describes a V-type internal combustion engine with an asymmetrical firing order and an independent A-side common rail system and an independent B-side common rail system. The conditions for an asymmetrical firing order are met, when, for example, the cylinder A1, i.e. the first cylinder on the A side, is ignited; and thereafter the cylinder A2, i.e. the second cylinder on the A side, is ignited. The asymmetrical firing order in turn causes pressure variations in the rail. In order to solve this problem, DE 10 2007 034 317 A1 proposes an equalization line between the two rails in a first solution. In a second solution the rail pressure on the A side is regulated with a proportional-integral (PI) controller in a closed loop rail pressure control circuit on the A side; and the rail pressure on the B side is regulated with a proportional (P) control in a closed loop rail pressure control circuit on the B side. Owing to the lack of an integral (I) component on the B side in the controller, this solution is critical with respect to a steady state system deviation.